Hydrogenation of glycolic acid

ABSTRACT

Glycolic acid is hydrogenated in the liquid phase in the presence of a catalyst consisting essentially of metallic cobalt and thorium oxide.

BACKGROUND OF THE INVENTION

This invention relates to a catalyst particularly suited for use incatalyzing the liquid phase reduction of glycolic acid to ethyleneglycol.

It is known to produce ethylene glycol by the liquid phase directhydrogenation of glycolic acid in the presence of a catalyst asdescribed, for example, in U.S. Pat. No. 2,607,805. It is also known touse metallic cobalt, either alone or in combination with various metaladditives, as a hydrogenation catalyst as described, for example, inU.S. Pat. Nos. 2,322,099; 3,260,683; 3,478,112; 3,772,395; and3,848,003.

Glycolic acid, however, tends to react with metallic cobalt to formcobalt glycolate. Although the cobalt glycolate may be reduced undertypical hydrogenation reaction conditions with redeposition of cobaltmetal, it has been observed that the catalytic activity of theredeposited cobalt metal is diminished resulting in decreased yields ofand decreased selectivity to ethylene glycol.

In order to minimize the extent of reaction between metallic cobalt andglycolic acid, it is desirable to provide a cobalt-based catalyst thatwould enable conversion of glycolic acid to ethylene glycol in as shortas possible a reaction time.

SUMMARY OF THE INVENTION

Ethylene glycol is prepared by hydrogenating glycolic acid in the liquidphase in the presence of a catalytically effective amount of a catalystconsisting essentially of metallic cobalt and thorium oxide.

DESCRIPTION OF THE INVENTION

In accordance with this invention, a combination of metallic cobalt andthorium oxide has been found to be particularly effective in catalyzingthe liquid phase hydrogenation of glycolic acid to ethylene glycol. Thecatalyst of the invention, in addition to being highly selective toethylene glycol, enables the production of ethylene glycol in highyields and in a shorter reaction time than cobalt alone or various othermetal promoted cobalt catalysts under substantially the same reactionconditions.

The catalyst of the invention may be prepared by precipitating cobaltand thorium preferably as their oxalates or carbonates from an aqueoussolution of cobalt and thorium salts. The precipitate is recovered fromthe solution, dried, pulverized, and heated in a hydrogen atmosphere toconvert the cobalt oxalate or carbonate to metallic cobalt and thethorium oxalate or carbonate to thorium oxide. The thorium oxide contentof the catalyst may vary from about 5 percent to about 20 percent byweight and preferably from about 10 percent to about 15 percent byweight thorium oxide with the balance metallic cobalt.

Any water soluble cobalt or thorium salts may be used to prepare thesolution from which the cobalt and thorium are precipitated as theiroxalates or carbonates, such as, for example, cobalt acetate, cobaltnitrate, cobalt chloride, cobalt sulfate, thorium nitrate, thoriumchloride, thorium sulfate, or the like. The cobalt and thorium areprecipitated as their oxalates or carbonates by the addition to thesolution of oxalic acid, sodium carbonate, potassium carbonate, or thelike.

Alternatively, other than precipitating the soluble cobalt and thoriumsalts as their oxalates or carbonates, substantially water insolublethorium or cobalt compounds may be physically mixed in the dry state andreduced. If, however, insoluble cobalt or thorium compounds are used asstarting materials, it is preferred that they first be slurried in waterto assure intimate mixing. After slurrying, the solids are separated,dried, and reduced as described hereinabove. Some suitable,substantially nonwater soluble thorium and cobalt compounds are, forexample, cobalt oxide, cobalt hydroxide, cobalt carbonate, cobaltoxalate, thorium oxalate, thorium oxide, thorium hydroxide, thoriumcarbonate, and the like.

The catalyst of the invention may be used with or without a support. Ifa continuous glycolic acid hydrogenation process is contemplated, it ispreferred to use a supported catalyst whereas an unsupported catalyst issatisfactory for use in a batch process. The supported catalyst may beprepared by slurrying the support material along with and depositing thecobalt and thorium oxides, oxalates, carbonates or hydroxides on thesupport material and subjecting the same to a reducing atmosphere at anelevated temperature. Typically, the supported catalyst, afterreduction, contains from about 10 percent to 80 percent, usually fromabout 40 percent to 60 percent, by weight of catalytic actives, i.e.,metallic cobalt and thorium oxide, based on the total weight ofcatalytic actives and support material.

With regard to the choice of support material, those having high alkalimetal, alkaline earth metal, or alumina contents have been found to beunsatisfactory since these tend to react with glycolic acid to formglycolates that are not readily reducible under ordinary liquid phasehydrogenation conditions. Consequently, silica or highly siliceousmaterials, i.e., those having a silica content of at least about 80percent by weight, are preferred, such as, for example, kieselguhr orthe like.

The liquid phase hydrogenation of glycolic acid using the catalyst ofthe invention may be conducted either batchwise or continuously.

In a typical batch reaction, a dilute, i.e., a 10 to 50 percent andusually about a 20 percent by weight, aqueous glycolic acid solution ischarged along with the catalyst to an autoclave reactor provided withstirring means. The glycolic acid is contacted with elemental hydrogenat a temperature of from about 150° C. to about 220° C., preferably fromabout 180° C. to about 190° C. at a hydrogen pressure of from about2,000 psig to about 10,000 psig, preferably from about 3,000 psig toabout 5,000 psig. The reaction is continued with stirring until hydrogenuptake substantially ceases, usually from about 20 minutes to one hour.The catalyst is separated from the reaction mixture by, for example,filtration, and the ethylene glycol is recovered from the reactionmixture by conventional means, for example, fractional distillation.

In the batch hydrogenation of glycolic acid, sufficient catalyst ispreferably used, whether supported or unsupported, to provide a molarratio of metallic cobalt to glycolic acid of at least about 0.8. At ametallic cobalt to glycolic acid mole ratio of less than about 0.8, ithas been observed that both the rate of conversion of glycolic acid andthe yield of ethylene glycol are somewhat diminished. Although highermetallic cobalt to glycolic acid molar ratios may be used, nosignificant increase in either the rate of conversion of glycolic acidor ethylene glycol yield is observed at molar ratios in excess of about1.3. Consequently, it is contemplated that in a batch hydrogenation themost beneficial results will obtain at metallic cobalt to glycolic acidmolar ratios of from about 0.8 to about 1.3 with an apparent optimum atabout 1.0 mole of metallic cobalt per mole of glycolic acid undergoinghydrogenation.

In a typical continuous hydrogenation process, aqueous glycolic acidsolution and hydrogen gas are fed to a vertical reactor and passedthrough a bed of catalyst under substantially the same conditions oftemperature and pressure at which the batch hydrogenation is conducted.When used in a continuous hydrogenation process, the catalyst ispreferably carried on a support as described hereinabove and ispreferably of a somewhat larger particle size, i.e., about 1 to 6millimeters, than the relatively finely divided catalyst, i.e., about100 to 400 mesh, typically used in the batch hydrogenation process.

In either the batch or continuous hydrogenation process, to furtherretard the tendency of the glycolic acid to react with the cobalt in thecatalyst, it has been found to be advantageous to dilute the glycolicacid with both ethylene glycol and water rather than to use water aloneas a diluent for the glycolic acid. A hydrogenation reaction mixturecontaining about 20 weight percent glycolic acid, about 70 weightpercent ethylene glycol, and about 10 weight percent water has beenfound to be particularly efficacious and it is contemplated thatbeneficial results would obtain using hydrogenation reaction mixturescontaining from about 10 to 40 weight percent glycolic acid, 5 to 20weight percent water, and the balance ethylene glycol. It is alsocontemplated that ethylene glycol alone be used as a diluent for theglycolic acid. If a glycolic acid/ethylene glycol hydrogenation reactionmixture is used, the glycolic acid may, if desired, be esterified priorto reduction.

The invention is further illustrated but is not intended that it belimited by the following examples.

EXAMPLE 1 Preparation of Catalysts

A. 1,000 milliliters of an aqueous solution containing 126 grams ofammonium dichromate [(NH₄)₂ Cr₂ O₇ ] and 278 milliliters of 28 percentaqueous ammonium hydroxide solution were mixed with 1,000 milliliters ofan aqueous solution containing 249 grams of cobaltous acetate [Co(C₂ H₃O₂)₂.4H₂ O] at a temperature of 70° C. The resulting precipitate wasrecovered by suction filtration and dried to constant weight. 56 gramsof the dried precipitate were ground to a powder and heated in ahydrogen gas stream at 530° C. to yield 35.1 grams of catalystcontaining 54 weight percent metallic cobalt.

B. 70.5 grams cobaltous carbonate [CoCO₃ ], 15.5 grams cupric acetate[Cu(C₂ H₃ O₂)₂.H₂ O], 22.5 grams manganous acetate [Mn(C₂ H₃ O₂)₂.4H₂O], and 9.4 grams ammonium molybdate [(NH₄)₆ Mo₇ O₂₄.4H₂ O] wereslurried with water, evaporated, and dried to constant weight. 22 gramsof the dried material were ground to a powder and heated in a hydrogengas stream at 400° C. to yield 17.1 grams of catalyst containing 66weight percent metallic cobalt.

C. 1,000 milliliters of an aqueous solution of oxalic acid dihydratewere mixed with 1,000 milliliters of an aqueous solution containing 247grams cobaltous acetate, 27.8 grams ferrous sulfate [FeSO₄.7H₂ O], 18.5grams nickel formate dihydrate [Ni(CHO₂)₂.2H₂ O], and 20 grams cupricacetate at a temperature of 50° C. The resultant precipitate wasrecovered by suction filtration and dried to constant weight. 64.3 gramsof the dried material were ground to a powder and heated in a hydrogengas stream at 455° C. to yield 20.6 grams of catalyst containing 76weight percent metallic cobalt.

D. 1,000 milliliters of an aqueous solution containing 148 gramscobaltous acetate, 32 grams cupric acetate, 11 grams manganous acetate,and 2.4 grams of 85 percent phosphoric acid were mixed with 1,000milliliters of an aqueous solution containing 101 grams oxalic aciddihydrate at a temperature of 50° C. The resultant precipitate wasrecovered by suction filtration and dried to constant weight. 65.2 gramsof the dried material were ground to a powder and heated in a hydrogengas stream at 440° C. to yield 212 grams of catalyst containing 73weight percent metallic cobalt.

E. 1,000 milliliters of an aqueous solution containing 249 gramscobaltous acetate, 18.5 grams nickel formate dihydrate, 10.1 gramscupric acetate, 5.0 grams ammonium dichromate, and 12.3 grams manganousacetate were mixed with 1,500 milliliters of an aqueous solutioncontaining 202 grams ammonium bicarbonate. The resulting precipitate wasrecovered by suction filtration. 50 milliliters of an aqueous solutioncontaining 5 grams ammonium molybdate and 5 grams polyphosphoric acidwere thoroughly mixed with the wet filter cake and the cake was dried toconstant weight. 38.2 grams of the dried solids were ground to a powderand heated in a hydrogen gas stream at 440° C. to yield 20.1 grams ofcatalyst containing 77 weight percent metallic cobalt.

F. 500 milliliters of an aqueous solution containing 125 grams cobaltousacetate were mixed with 500 milliliters of an aqueous solutioncontaining 79 grams ammonium bicarbonate. The resulting precipitate wasrecovered by suction filtration and 50 milliliters of an aqueoussolution containing 10.6 grams molybdic acid and 8.3 grams 28 percentammonium hydroxide solution were thoroughly mixed with the wet filtercake. The cake was dried to constant weight and 30 grams of the driedmaterial were ground to a powder and heated in a hydrogen gas stream at400° C. to yield 17.3 grams of catalyst containing 91 weight percentmetallic cobalt.

G. 600 milliliters of an aqueous solution containing 176 grams ammoniummolybdate and 138 grams 28 percent ammonium hydroxide solution weremixed with 1,000 milliliters of an aqueous solution containing 249 gramscobaltous acetate. The resulting precipitate was recovered by suctionfiltration and dried to constant weight. 64.1 grams of the driedmaterial were ground to a powder and heated in a hydrogen gas stream at700° C. to yield 42.0 grams of catalyst containing 37 weight percentmetallic cobalt.

H. 19.8 grams of powdered cobaltous oxide (CoO) prepared from cobaltousoxalate (CoC₂ O₄) which had been sintered at 1050° C. were heated in ahydrogen gas stream at 500° C. 14.9 grams of metallic cobalt wasobtained which was mixed with 10 grams of CALSICAT®, a commercialcatalyst composition containing about one weight percent platinum oncarbon.

I. 30 grams of CELITE® 545 silica (Fisher Scientific Co. C-212) wasadded to 1,000 milliliters of an aqueous solution containing 125 gramscobaltous acetate. The solution was heated to 65° C. and mixed with1,000 milliliters of an aqueous solution containing 103.6 gramspotassium carbonate also heated to 65° C. The resulting precipitate wasrecovered by suction filtration and dried to constant weight. 42.3 gramsof the dried material were ground to a powder and heated in a hydrogengas stream at 400° C. to yield 29.4 grams of a supported catalystcontaining 50 weight percent metallic cobalt.

J. 15 grams of CELITE® 545 was added to 150 milliliters of an aqueoussolution containing 62 grams cobaltous acetate and evaporated to drynessunder reduced pressure. The solids were mixed with 150 milliliters of anaqueous solution containing 35 grams oxalic acid dihydrate. Theresultant precipitate was recovered by suction filtration and dried toconstant weight. 57.1 grams of the dried material were ground to apowder and heated in a hydrogen gas stream at 400° C. to yield 27.4grams of a supported catalyst containing 53 weight percent metalliccobalt.

K. 800 milliliters of an aqueous solution containing 164 grams cobaltousacetate, 4.9 grams thorium nitrate [Th(NO₃)₄.4H₂ O], and 38 gramsmagnesium acetate [Mg(C₂ H₃ O₂)₂.4H₂ O] were heated to 75° C. and mixedwith 800 milliliters of an aqueous solution containing 111 grams ofoxalic acid dihydrate. The resultant precipitate was recovered bysuction filtration and dried to constant weight. 76.8 grams of the driedmaterial were ground to a powder and heated in a hydrogen gas stream at430° C. to yield 26.8 grams of catalyst containing 77 weight percentmetallic cobalt.

L. 800 milliliters of an aqueous solution containing 164 grams cobaltousacetate and 9.8 grams thorium nitrate were heated to 55° C. and mixedwith 800 milliliters of an aqueous solution containing 92 grams ofoxalic acid dihydrate. The resultant precipitate was recovered bysuction filtration and dried to constant weight. 69 grams of the driedmaterial were ground to a powder and heated in a hydrogen gas stream at430° C. to yield 22.9 grams of catalyst containing 87 weight percentmetallic cobalt and 13 weight percent thorium oxide.

M. 19.5 grams of CELITE® 545 was added to 800 milliliters of an aqueoussolution containing 96 grams cobaltous nitrate [Co(NO₃)₂.6H₂ O] and 4.92grams thorium nitrate to which was added 800 milliliters of an aqueoussolution containing 53 grams potassium carbonate. The resultingprecipitate was recovered by suction filtration and dried to constantweight. 45.6 grams of the dried material were ground to a powder andheated in a hydrogen gas stream at 430° C. to yield 32.7 grams of asupported catalyst containing 47 weight percent metallic cobalt, 5.7weight percent thorium oxide, and the balance support material.

EXAMPLE 2 Hydrogenation of Glycolic Acid

A 300 cubic centimeter capacity stainless steel autoclave provided withstirring means (available from Autoclave Engineers, Inc.) was used asthe hydrogenation reactor. For each hydrogenation run using each of thecatalysts prepared in Example 1, the autoclave was charged under anitrogen atmosphere with 0.262 moles glycolic acid as a 20 weightpercent aqueous glycolic acid solution along with the respectivecatalyst. After charging with glycolic acid and catalyst, the autoclavewas sealed and pressurized to 3,000 psig with nitrogen for 30 minutes tocheck for leaks and then swept with hydrogen. The autoclave was thenbrought up to operating temperature and pressurized with hydrogen gas tothe desired operating pressure. Timing of the reaction was begun whenhydrogen uptake was initially observed. The reaction was continued withstirring until cessation of hydrogen uptake was observed, after whichthe autoclave was cooled, vented, and disassembled. The catalyst wasseparated from the reaction products by suction filtration and thefiltrate was submitted for analysis. The results and conditions ofglycolic acid hydrogenation runs using catalysts A through M aresummarized in Table I.

From an inspection of the data, it is seen that metallic cobalt alone(catalysts I and J) and certain of the catalysts containing metalliccobalt and metal additives (catalysts A and C) are effective incatalyzing the hydrogenation of glycolic acid. However, it is furtherseen that the catalyst of the invention (catalysts L and M) givessubstantially equivalent results in significantly shorter reaction timesand at lower temperatures. With regard to catalyst K, although thiscatalyst appeared to be very reactive initially, hydrogen uptake ceasedafter 10 minutes. It is believed that the magnesium in the catalystreacted with the glycolic acid to form a glycolate that was apparentlyunreducible under reaction conditions.

Although the invention has been described with specific references andspecific details of embodiments thereof, it is to be understood that itis not intended to be so limited since changes and alterations thereinmay be made by those skilled in the art which are within the fullintended scope of this invention as defined by the appended claims.

                                      TABLE I                                     __________________________________________________________________________    Catalytic Hydrogenation of Glycolic Acid                                                         Moles Cobalt        Reaction                                                                           Ethylene                                                                           Ethylene                          Catalyst      per Mole      Pressure,                                                                           Time,                                                                              Glycol, %                                                                          Glycol, %                    Catalyst                                                                           Composition   Glycolic Acid                                                                         Temp. ° C.                                                                   psig  minutes                                                                            Yield Of                                                                           Selectivity                  __________________________________________________________________________                                                     To                           A    Co + Cr       1.20    225   3500-4100                                                                           139  92   96                           B    Co + Cu + Mn + Mo                                                                           0.73    250   3800-4000                                                                           50   38   100                          C    Co + Fe + Ni + Cu                                                                           1.02    234   3500-4100                                                                           49   95   96                           D    Co + Cu + Mn + P                                                                            1.00    227   3500-4100                                                                           49   77   100                          E    Co + Ni + Cu + Mn + Cr                                                                      1.00    244   3500-4100                                                                           142  85   86                           F    Co + Mo       1.02    251   3600-4400                                                                           74   32   84                           G    Co + Mo       1.01    245   3500-4100                                                                           58   45   64                           H    Co + Pt       0.93    226   4200-4400                                                                           30   9    73                           I    Co            0.96    226   3500-4100                                                                           66   96   93                           J    Co            0.94    230   3500-4100                                                                           45   95   91                           K    Co + ThO.sub.2 + MgO                                                                        1.32    187   3000-3400                                                                           10   40   83                           L    Co + ThO.sub.2                                                                              1.24    209   3500-4200                                                                           23   92   94                           M    Co + ThO.sub.2                                                                              1.00    188   3500-4000                                                                           30   94   95                           __________________________________________________________________________

I claim:
 1. In a process for producing ethylene glycol by catalyticliquid phase hydrogenation of glycolic acid, the improvement comprisinghydrogenating glycolic acid in the presence of a catalyst consistingessentially of metallic cobalt and from about 5 to 20 percent by weightthorium oxide based on the combined weight of metallic cobalt andthorium oxide.
 2. The improved process of claim 1 wherein the catalystcontains from about 10 to about 15 percent by weight thorium oxide basedon the combined weights of metallic cobalt and thorium oxide.
 3. Theimproved process of claim 1 wherein the metallic cobalt and thoriumoxide are carried on a particulate support containing at least about 80percent silica.